Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C1/00—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon
  • C07C1/02—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon
  • C07C1/04—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon from carbon monoxide with hydrogen
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
  • F25J3/0252—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of hydrogen
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C7/00—Purification; Separation; Use of additives
  • C07C7/04—Purification; Separation; Use of additives by distillation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C7/00—Purification; Separation; Use of additives
  • C07C7/09—Purification; Separation; Use of additives by fractional condensation
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G70/00—Working-up undefined normally gaseous mixtures obtained by processes covered by groups C10G9/00, C10G11/00, C10G15/00, C10G47/00, C10G51/00
  • C10G70/04—Working-up undefined normally gaseous mixtures obtained by processes covered by groups C10G9/00, C10G11/00, C10G15/00, C10G47/00, C10G51/00 by physical processes
  • C10G70/041—Working-up undefined normally gaseous mixtures obtained by processes covered by groups C10G9/00, C10G11/00, C10G15/00, C10G47/00, C10G51/00 by physical processes by distillation
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
  • F25J3/0219—Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
  • F25J3/0233—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 1 carbon atom or more
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
  • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
  • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
  • F25J3/0238—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of CnHm with 2 carbon atoms or more
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2200/00—Processes or apparatus using separation by rectification
  • F25J2200/70—Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2200/00—Processes or apparatus using separation by rectification
  • F25J2200/74—Refluxing the column with at least a part of the partially condensed overhead gas
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2205/00—Processes or apparatus using other separation and/or other processing means
  • F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
  • F25J2205/04—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum in the feed line, i.e. upstream of the fractionation step
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2210/00—Processes characterised by the type or other details of the feed stream
  • F25J2210/12—Refinery or petrochemical off-gas
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2215/00—Processes characterised by the type or other details of the product stream
  • F25J2215/60—Methane
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2215/00—Processes characterised by the type or other details of the product stream
  • F25J2215/62—Ethane or ethylene
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2270/00—Refrigeration techniques used
  • F25J2270/12—External refrigeration with liquid vaporising loop
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2270/00—Refrigeration techniques used
  • F25J2270/18—External refrigeration with incorporated cascade loop
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2270/00—Refrigeration techniques used
  • F25J2270/66—Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2270/00—Refrigeration techniques used
  • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
  • F25J2270/902—Details about the refrigeration cycle used, e.g. composition of refrigerant, arrangement of compressors or cascade, make up sources, use of reflux exchangers etc.
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P30/00—Technologies relating to oil refining and petrochemical industry
  • Y02P30/40—Ethylene production

Definitions

• the present invention pertains to a refrigeration system to provide the cooling requirements of an ethylene plant. More particularly, the invention is directed to the use of a binary refrigerant comprising a mixture of methane and ethylene for cooling in an ethylene plant.
• Ethylene plants require refrigeration to separate out desired products from the cracking heater effluent.
• a C 3 refrigerant usually propylene
• a C 2 refrigerant typically ethylene
• a separate methane refrigeration system is also employed.
• three separate refrigeration systems are required, cascading from lowest temperature to highest.
• Three compressor and driver systems complete with suction drums, separate exchangers, piping, etc. are required.
• a methane refrigeration cycle often requires reciprocating compressors which can partially offset any capital cost savings resulting from the use of low pressure demethanizers.
• Mixed refrigerant systems have been well known in the industry for many decades. In these systems, multiple components are utilized in a single refrigeration system to provide refrigeration at a wider range of temperatures, enabling one mixed refrigeration system to replace multiple pure component cascade refrigeration systems. These mixed refrigeration systems have found widespread use in base load liquid natural gas plants.
• This system replaces the separate methane and ethylene refrigeration systems which are used in conjunction with a propylene refrigeration system in conventional plants and saves one compressor system.
• the refrigerant composition may be constant throughout the system or separators may be used to partially flash and divide the binary refrigerant into a methane rich stream and an ethylene rich stream for separate circulation in one or more heat exchangers.
• Figure 1 is a schematic flow diagram of a portion of an ethylene plant illustrating one embodiment of the refrigeration system of the present invention.
• Figure 2 is a schematic flow diagram similar to Figure 1 but illustrating an alternate embodiment of the invention.
• Figure 3 is a schematic flow diagram illustrating a variation of the Figure 2 embodiment.
• the present invention involves an ethylene plant wherein a pyrolysis gas is first processed to remove methane and hydrogen and then processed in a known manner to produce and separate ethylene as well as propylene and some other by-products.
• a pyrolysis gas is first processed to remove methane and hydrogen and then processed in a known manner to produce and separate ethylene as well as propylene and some other by-products.
• the separation of the gases in an ethylene plant through condensation and fractionation at cryogenic temperatures requires refrigeration over a wide temperature range.
• the capital cost involved in the refrigeration system of an ethylene plant can be a significant part of the overall plant cost. Therefore, capital savings for the refrigeration system will significantly affect the overall plant cost.
• Ethylene plants with high pressure demethanizers operate at pressures higher than 2.758 MPa (400 psi) and can produce overhead reflux by condensation against a pure component ethylene refrigeration.
• Demethanizer overhead temperatures of these systems are typically in the range of -85°C to -1 00°C.
• Ethylene refrigeration at approximately -1 01 °C is typically used for chilling the overhead condenser.
• the overhead temperature is typically too low to use ethylene refrigeration unless a vacuum suction is used. But that is not desirable because of the capital cost increase and the safety concern due to potential air leakage into the system.
• a low pressure demethanizer is one which operates below about 2.41 MPa (350 psi) and generally in the range of 0.345 to
• the binary refrigerant of the present invention comprises a mixture of methane and ethylene.
• the ratio of methane to ethylene will vary depending on ethylene plant cracking feedstock, cracking severity, chilling train pressure and the nature of the refrigerant among other considerations, but will normally be in the range of 1 0 : 90 to 50 : 50 and more likely in the range of 20 : 80 to 40 : 60.
• the use of the methane and ethylene or methane and ethane binary refrigerant, along with a propylene or propane refrigeration system, provides the refrigeration load and temperatures required for an ethylene plant having a low pressure demethanizer while obviating the need for three separate refrigerants of methane, ethylene and propylene.
• a binary refrigerant would not be used with a high pressure demethanizer because there is no need to provide that level of refrigeration. There is no need to use a binary refrigeration system as a simple substitute for a pure component ethylene refrigeration system. It would just be more costly and complex.
• Mixed refrigerant systems to replace both the ethylene and propylene refrigeration systems have been proposed but they require at least one component lighter than the ethylene such as methane. Therefore, it is at least a ternary system.
• the purpose of the present invention is to provide the necessary refrigeration for the charge gas (pyrolysis gas) in general to separate out the hydrogen and methane and provide a feed for the demethanizer.
• the charge gas feed 2 which is the pyrolysis gas conditioned as required and cooled, is typically at a temperature of about -35 to -37°C and a pressure of about 3.45 MPa (500 psi), and is typically already partially liquified.
• the charge gas 2 is progressively cooled by the refrigeration system of the present invention in the heat exchangers 4, 6, 8 and 1 0 and separated to produce demethanizer feeds as will be explained later.
• the heat exchangers 4, 6, 8 and 1 0 are typically brazed aluminum exchangers, also called platefin or core exchangers, and can be physically combined as fewer units or expanded into a greater number of units.
• the C, and lighter components primarily methane and hydrogen, are separated from the C 2 and heavier components.
• the net overhead 14 from the demethanizer 1 2 is used as a cooling stream in the refrigeration system as will be explained hereinafter.
• the bottoms 1 6 from the demethanizer can also be used as a cooling stream in another portion of the refrigeration system as will also be explained hereinafter.
• the binary refrigerant as identified earlier as a mixture of methane and ethylene is compressed by the refrigeration compressor 1 8 up to a pressure in the range of about 3.0 to 4.0 MPa.
• specific pressures and temperatures for one specific example of the invention are listed.
• the compressed binary refrigerant 20 is cooled at
• the liquid binary coolant is collected in the receiver or accumulator 28.
• the coolant 30 from the receiver 28 can be further cooled at 32 by heat exchange with the bottoms 1 6 from the demethanizer 1 2, or other cold stream being heated, which will lower the temperature.
• the demethanizer bottoms exiting from the heat exchanger 32 at 34 are sent to the deethanizer for the conventional production and separation of the ethylene, propylene and other by-products.
• the binary refrigerant 36 from the heat exchanger 32 is then passed to the first of the series of the heat exchangers 4, 6, 8, 1 0 and 1 1 .
• the heat exchangers 4 to 10 are the heat exchangers which provide the cooling of the charge gas from the pyrolyzer. Heat exchanger 1 1 provides reflux to the demethanizer.
• the binary refrigerant 36 is passed through the heat exchange coil 46 and cooled. A portion of the binary refrigerant is then withdrawn at 48 and the temperature is dropped by lowering the pressure through the expansion valve 50. This cooled binary refrigerant portion is then passed back through the heat exchange coil 52.
• the expansion valve 50 is controlled in response to the temperature of the charge gas stream 54 cooled in the heat exchanger 4 thereby controlling the temperature of the refrigerant in the heat exchange coil 52.
• the binary refrigerant in heat exchange coil 52 absorbs heat and is vaporized and superheated up to a temperature range of 1 to 5°C lower than incoming stream 36.
• the vaporized binary refrigerant 56 from the coil 52 passes to the suction drum 58 from which the refrigerant vapor stream 60 is fed to the binary refrigeration compressor 1 8.
• the suction drum 58, as well as the other suction drums 84, 102 and 1 30 referred to later, is present only to separate out any liquid that may be present in an upset condition to prevent potential compressor damage. It is not needed for the normal operation of the system.
• the reason that the binary refrigerant is first passed through the heat exchanger 4 for cooling before flashing at 50 is to decrease the percentage of vapor flashed at a fixed flash pressure.
• the flashed liquid will be colder and can provide more refrigeration at colder temperatures.
• the flashed liquid temperature is fixed for any given flashed liquid pressure and there would be no net gain from cooling before flashing. This same principal applies to the other heat exchangers 6, 8, 10 and 1 1 .
• Additional cooling in the heat exchanger 4 as well as in the other heat exchangers 6, 8 and 1 0 is provided by the streams 62, 64 and 66 which are low temperature streams of hydrogen, low pressure methane and high pressure methane respectively. These low temperature streams 62, 64 and 66 come from the cryogenic hydrogen/methane separation system 68 and the overhead 1 4 from the demethanizer 1 2. The net overhead stream 66 also provides chilling for heat exchanger 1 1 which serves as a demethanizer reflux condenser.
• the cooled charge gas 54 may be further cooled at 70 and fed to the next heat exchanger 6.
• the cooling at exchanger 70 can be reboiling and interboiling of demethanizer 1 2.
• the remaining cooled binary refrigerant 72 from the heat exchanger 4 is also fed to the next heat exchanger 6.
• This heat exchanger 6 is operated in the same manner as the heat exchanger 4 except that all of the relevant temperatures are now lower including the temperatures of the incoming binary refrigerant stream 72, the exit binary refrigerant stream 74, the binary refrigerant stream 76 after the expansion valve 78, the vaporized binary refrigerant stream 80 from the coil 81 and the exit charge gas stream 82.
• the vaporized binary refrigerant 80 is fed to the suction drum 84 and then fed at 86 to the binary refrigeration compressor 1 8.
• the charge gas stream 82 is fed to the separator 88 in which the cooled charge gas is separated into a less volatile demethanizer feed stream 90 and a more volatile overhead stream 92 which is now more concentrated in methane and hydrogen.
• the overhead 92 and the binary refrigerant 74 pass to the next heat exchanger 8 wherein the cooling process continues in the same manner producing the further cooled charge gas 94 and binary refrigerant 96.
• a portion of the binary refrigerant passes through the expansion valve 98 and the coil 100 to the suction drum 102.
• the vapor 104 is then fed to the binary refrigerant compressor 1 8.
• the heat exchanger 8 may also be further cooled by the vaporized binary refrigerant stream 106 from the heat exchanger 10.
• the charge gas 94 from the heat exchanger 8 is fed to the separator 108 where the more volatile components are removed overhead at 1 10 and fed to the heat exchanger 10. This overhead is now even further concentrated in hydrogen and methane.
• the bottoms from the separator 1 08 are fed at 1 1 2 to the demethanizer 1 2.
• the cooling process continues in the heat exchanger 10 by the expansion of an additional portion of the binary refrigerant through the expansion valve 1 1 4 and the vaporization in coil 1 1 6 to produce the binary refrigerant stream 1 06 previously mentioned.
• the exit charge gas 1 18 is fed to the separator 1 20 with the overhead 1 22 now being primarily hydrogen and methane.
• the overhead 1 22 is fed to the hydrogen/methane separation system 68 where the hydrogen and methane are cryogenically separated to produce the hydrogen stream 62 and the low pressure methane stream 64.
• the bottoms from the separator 1 20 are fed at 1 24 to the demethanizer 1 2.
• the now remaining binary refrigerant stream 1 26 is further cooled in the heat exchanger 1 1 by the demethanizer net overhead 66.
• the binary refrigerant stream 1 26 is expanded at 1 33 and passed back through the coil 1 35 in heat exchanger 1 1 to be mixed with the refrigerant from valve 1 14.
• the gross overhead stream 14 from the demethanizer 12 goes to the heat exchanger 1 1 where it is partially condensed.
• This partially condensed stream 1 27 flows to the separator 1 28.
• Liquid 1 29 from the separator 128 flows back to the demethanizer 12 as reflux.
• the overhead 66 from separator 1 28 is now the net demethanizer overhead comprising primarily methane which is reheated by passing back through the heat exchangers 1 1 , 10, 8, 6 and 4.
• the demethanizer column 1 2 has the typical reboiler and interreboilers between stages which have not been shown.
• the bottoms 1 6 of the demethanizer is C 2 and heavier components.
• Reboiling and interreboiling are typically provided by cooling of the charge gas such as by the heat exchanger 70.
• Stream 1 06 goes to suction drum 1 30 and then at 1 32 to the binary refrigerant compressor 1 8.
• Figure 1 illustrates four heat exchangers 4, 6, 8 and 1 0, the number of these heat exchangers can vary depending on the particular needs for any particular ethylene process and in particular on the particular charge gas.
• the following Table lists temperatures and some pressures for the binary refrigerant and for the charge gas (process gas) including the demethanizer system at various locations in the process flow scheme of Figure 1 for one specific example:
• the binary refrigerant system of the present invention has been previously mentioned and include a reduction in the number of compressor systems and the ability to use all centrifugal or axial compressors instead of a methane reciprocating compressor.
• a further advantage is that the binary refrigerant composition is easier to maintain than a more complicated mixed refrigerant containing three or more components. This is most evident in the event of a system trip or upset which results in the venting of refrigerant. The venting process results in the loss of more of the lighter components of the refrigerant than of the heavier components. This changes the ratio of the components which must be corrected upon re- start. The more complicated the refrigerant composition, the more difficult it is to correct the ratio.
• an expansion valve 1 36 is located in the line 36.
• the pressure of the binary refrigerant drops and a portion is vaporized.
• the liquified portion and the vapor portion are separated in the flash tank
• the methane-rich stream 1 40 passes through all of the heat exchangers 4, 6, 8 and 1 0 and a portion is then expanded at 144 and passed back as stream 146 through all of the heat exchangers 10,
• 142 is handled somewhat like the binary refrigerant stream in Figure 2 in that a portion is withdrawn after each of the first three heat exchangers at 148, 1 50 and 1 52 and expanded at 1 54, 1 56 and 1 58. The expanded portions are then passed back through one or more of the heat exchangers to produce the exit ethylene- or ethane-rich binary refrigerant stream 1 60, 1 62 and 1 64 which are fed back to the appropriate compressor stages.
• a variation of Figure 2 has no valve 1 36 in line 36. Rather, the pressure in line 36 is lowered such that the stream is not completely liquified and a vapor portion remains. Separator 1 38 separates the condensed liquid portion from the methane-enriched vapor portion.
• This variation allows compressor 1 8 to have a lower discharge pressure for any given methane-ethylene (or methane-ethane) composition for stream 36. The overall compression ratio for compressor 1 8 is lowered. The flow rate of stream 36 increases to compensate for any given stream 36 composition. Compressor costs can however decrease. This scheme is particularly of interest for smaller ethylene plants where the actual compressor volume at the discharge of compressor 1 8 approaches the lower limit allowable by centrifugal compressor design.
• FIG 3 is a still further modification of the present invention similar to the embodiment shown in Figure 2 but with an additional separation step for the binary refrigerant.
• the methane-rich binary refrigerant vapor stream 140 is passed through the heat exchanger 4, partially liquified, and then passes through the line 1 66 to the additional refrigerant separator 1 70 where the refrigerant is again separated into a second methane-rich vapor stream 1 72 and a second ethylene- or ethane-rich liquid stream 1 74.
• the methane-rich stream 1 72 will be richer in methane than stream 1 74 and stream 1 40.
• the ethylene- or ethane-rich stream 142 passes through the heat exchangers just as in the Figure 2 embodiment.
• the second methane-rich stream 1 72 is passed through the second heat exchanger 6, and then flows to lower temperature heat exchangers as in the other embodiments where it is expanded and passed back through the heat exchangers.
• the second ethylene- or ethane-rich stream 1 74 is passed through the second heat exchanger, expanded at 1 78 and passed back through the heat exchanger.
• This Figure 3 illustrates only two heat exchangers for simplicity but there could be additional heat exchangers and additional separators similar to separator 1 70.

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• Oil, Petroleum & Natural Gas (AREA)
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• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
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• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Fats And Perfumes (AREA)
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• Compression-Type Refrigeration Machines With Reversible Cycles (AREA)
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• 1998
  • 1998-01-06 US US09/003,432 patent/US5979177A/en not_active Expired - Lifetime
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  • 1998-12-29 AU AU20178/99A patent/AU2017899A/en not_active Abandoned
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  • 1998-12-29 WO PCT/US1998/027700 patent/WO1999035110A1/fr active IP Right Grant
  • 1998-12-29 EP EP98964969A patent/EP1045820B1/fr not_active Expired - Lifetime
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